Something I found interesting from this week's reading are places that aren't known for their seismic activity, yet have experienced many earthquakes in the past, sometimes at destructive levels. Two places that come to mind in the U.S. are the New Madrid zone and the Coastal Plain of South Carolina. Below is a map illustrating the frequency of earthquakes in these areas; it's the same map from our book.
You don't typically think of these places as being prone to earthquakes, as they aren't even located near major faults. Yet from 1811-1812, the New Madrid zone famously experienced three major earthquakes at magnitudes from 8.1-8.3 (Foresman 291).
First I wondered if these areas are located over "mini hotspots"- relatives to the bigger hotspots that form volcanoes, such as those that make up the Hawaiian islands. That would have explained the frequent earthquake activity, as volcanoes have been known to generate seismic activity. However, the lack of volcanic activity in these areas poses a problem for that hypothesis.
Then I did some research and found that under the New Madrid zone is a buried rift, where seismic activity "may be produced by movement on old faults in response to compressive stress related to plate motions" (USGS). More mysterious is South Carolina's seismic zone. In 1886, Charleston experienced an estimated 7.6 earthquake (SCGS), which amazes me! It was the strongest earthquake in recorded history to ever hit the eastern seaboard. Geologists suspect the faults in South Carolina are "hidden by a thick sequence of sediments" (SCGS).
It's harder to predict earthquakes in areas like these because there are so few surface features that would indicate earthquake activity. Yet it's important to monitor them because they can surprise people living in populated areas who wouldn't normally expect earthquakes to happen.
Foresman, Timothy & Strahler, Alan H. 2012. Visualizing Physical Geography, 2nd ed. John Wiley & Sons, Inc. Hoboken, New Jersey.
USGS- United States Geological Survey. The New Madrid Seismic Zone. Retrieved from https://www.usgs.gov/natural-hazards/earthquake-hazards/science/new-madrid-seismic-zone?qt-science_center_objects=0#qt-science_center_objects
SCGS- South Carolina Geological Survey. Retrieved from https://www.dnr.sc.gov/geology/earthquake-info.html
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